The true antioestrogen, 1,1,2,2-tetramethyl-1,2-bis-(4-hydroxyphenyl)-ethane (R. W. Hartmann, Eur. J. Cancer Clin. Oncol. 1983, 19 959), shows considerable affinity for the oestrogen receptor (relative binding affinity=3.6). This compound shows for example a strong effect as antioestrogen by inhibiting the oestrone- or oestradiol-stimulated uterus growth of juvenile mice and inhibits the growth of the mammary carcinoma induced in rats (Sprague Dawley rats) by 7,12-dimethylbenzanthracene (DMBA), an experimental tumor which is very similar in its behavior to the human mammary carcinoma (MC).